For a conventional solid-state imaging device having a photodiode in a semiconductor substrate, minimization of a pixel size reaches its limit, making it difficult to improve performance such as sensitivity and the like. Accordingly, there has been suggested a solid-state imaging device which is highly sensitive stack type, and enables to obtain 100% aperture ratio by installing a photoelectric conversion layer on the upper part of a semiconductor substrate (Patent Document 1).
The stack type solid-state imaging device as disclosed in Patent Document 1 has a constitution where a plurality of pixel electrodes are arrayed on the upper part of a semiconductor device, a light receiving layer which includes an organic material (including at least a photoelectric conversion layer) is formed on the upper part of the plurality of pixel electrodes, and a counter electrode is formed on the upper part of the light receiving layer. The solid-state imaging device applies an electric field to the light receiving layer by applying a bias voltage to the counter electrode, and transfers the electric charge generated in the light receiving layer to the pixel electrode. Then, the stack type solid-state imaging device reads out a signal corresponding to the electric charge by a reading circuit which is connected to the pixel electrode.
In the stack type solid-state imaging device, after a pixel electrode, a light receiving layer and a counter electrode are formed, a protective film, a color filter, other functional films and the like may be formed on the upper part thereof in some cases so as to block the outside air (water and oxygen). In the case of a color filter, for example, along with a process of applying chemicals, a heating process is generally performed at 200° C. with respect to the light receiving layer for curing.
In addition, the heating process is also performed in cases of wire bonding for electrically connecting a circuit board and a package, a die bonding of a chip for package and reflow soldering for connecting a package to an IC substrate. Further, for the wire bonding, it is required to install a PAD opening on the periphery of a chip and the like, and in this case, forming a registor pattern or etching is performed, and at each process, heating process is performed for the substrate where a light receiving layer is formed.
As described above, in the case of manufacturing a solid-state imaging device using a light receiving layer that includes an organic material, a high-temperature heating process is required when adopting a processing method used in a conventional silicon device. A light receiving layer is required to be resistant to such heating process.
As a method for improving heat resistance of a light receiving layer, it is common to use a material having a little heat change (for example, a material having a high glass transition Tg). However, a light receiving layer is also required to have properties such as high photoelectric conversion efficiency and a low dark current, in addition to heat resistance. Accordingly, it is necessary to choose a material that satisfies those properties and heat resistance, which narrows the choice range of a material of a light receiving layer.
As described above, many methods have been suggested to improve heat resistance of a light receiving layer. However, it has not been known to improve heat resistance with the focus on other constituent elements than a light receiving layer.
Further, not only a solid-state imaging device, but also other devices such as a solar cell using a light receiving layer have the problem of heat resistance if the heating process is performed after a light receiving layer is formed.
Patent Documents 2 and 4 disclose a method for manufacturing a photoelectric conversion device in which an ITO film is formed on a glass substrate by a sputtering method, and after patterning is performed to form a pixel electrode, the substrate is heated and dried at 250° C., and then a light receiving layer and a counter electrode are formed.
However, the manufacturing method only provides heating at 250° C. for drying the ITO pixel electrode, without the aim of improving heat resistance. In addition, the method does not describe the specific range of temperatures for improving heat resistance of a photoelectric conversion device having a light receiving layer that includes an organic material.
Moreover, Patent Document 5 describes a thin film solar cell in which after Ag electrode is formed on a polyimide substrate, heating is performed at 230° C. before forming an a-Si photoelectric conversion layer.
However, the method relates to an inorganic solar cell, and does not describe the specific range of temperatures for improving heat resistance of a photoelectric conversion device having a light receiving layer that includes an organic material.